The present disclosure relates generally to a method of forming nanoscale structures, and more particularly to a method of inverting tones of two-dimensional self-assembled sublithographic nanoscale structures, and structures for implementing the same.
As integrated circuit densities have scaled, the use of grating based patterning techniques and unidirectional design has become an integral part of pattern formation technology. Grating fabrication can be effected using a variety of techniques including direct self-assembly, sidewall image transfer, pitch split lithography, extreme ultraviolet lithography, electron beam lithography, and interference lithography.
The grating pattern needs to be customized in order to form a circuit pattern. The ability to register customizing shapes to the grating pattern imposes a limitation on the spatial frequency (pitch) of the grating structure.
Directed self-assembly is a technique for forming a sublithographic line/space pattern utilizing the phase separation of a block copolymer thin film. The resolution and the critical dimension (CD) of the pattern are controlled by the composition of the copolymer. The methods of aligning the phase separated copolymers include chemical epitaxy and graphoepitaxy. The advantages of direct self-assembly include a high resolution of features at dimensions less than 10 nm, compatibility with existing lithography techniques, and the ability for frequency multiplication and space subdivision.
Directed self-assembly, however, requires a template layer to induce the alignment of phase separated polymers to the shape of the template layer. Thus, a pattern that can be formed by direct self-assembly alone is limited by requirements on the pattern of the template layer.